Auxiliary power unit heating system

ABSTRACT

An engine heating system for vehicles comprising an engine, a vehicle compartment heating system including fluid conduits extending from the engine to a heating unit and extending back to the engine, an auxiliary power unit on the vehicle including an auxiliary engine having a water pump driven by the auxiliary engine including fluid conduits extending from the auxiliary engine to a second heating unit located in a compartment of the vehicle and extending back to the auxiliary engine, fluid conduits extending from the engine to the second heating unit and extending back to the engine, a valve disposed in the fluid conduit between the second heating unit and the engine, the valve capable of receiving a signal, a temperature switch for detecting a coolant temperature, the temperature switch providing a signal to operate the valve, the valve allowing coolant circulation through the second heating unit to the main engine when the main engine is in operation or the coolant temperature is greater than a predetermined temperature, and the valve closed when the main engine is not in operation or the coolant temperature is below a predetermined temperature.

FIELD OF THE INVENTION

The invention relates to an auxiliary power unit heating system, and more particularly, to an auxiliary power unit heating system comprising a means for selectively isolating a cabin heating unit in the auxiliary power unit cooling system from a main engine coolant system while also providing heating capability for the main engine.

BACKGROUND OF THE INVENTION

Generally, large diesel engines are not shut down during cold weather conditions due to the difficulty in restarting. Diesel engines do not have the benefit of an electric spark to generate combustion and must rely on heat generated by compressing air to ignite fuel in the engine cylinders. In low temperature conditions (ambient temperatures below about 40° F.), two major factors contribute to the difficulty in starting a diesel engine. First, cold ambient air drawn into the engine must be increased in temperature sufficiently to cause combustion. Second, diesel fuel tends to exhibit poor viscous qualities at low temperatures, making engine starting difficult.

In cold weather, large engines are typically idled overnight to avoid the necessity to restart in the morning and to provide heat to the crew space. Diesel trucks that must operate in extremely cold environmental conditions must be run continuously, at high fuel cost, or, when shutdown, must be drained of engine coolant and provided supplemental electrical service and heating, also at high cost.

In warm weather, diesel engines typically idle to provide air conditioning and other services, including lighting, environmental heating and cooling, and electrical appliances.

Representative of the art is U.S. Pat. No. 4,756,359 to Greer (1988) which discloses a small lightweight auxiliary power plant including an engine, electrical alternator, water pump, air conditioning compressor and a heat exchanger is mounted at a convenient location on the tractor of a truck or other large vehicle. The main engine of the truck operates the existing truck air conditioning and heating system in a normal manner when the main engine is running. When the main engine of the truck is not operating and the smaller engine of the auxiliary power plant is operating, the truck air conditioning and heating system is operated by the auxiliary power plant. The heat exchanger of the auxiliary power plant then utilizes the heat of exhaust gases generated by the auxiliary power plant engine to warm the truck engine during the time it is not operating so that easy starting of the truck engine is made possible even in very cold weather. The exhaust gases from the auxiliary engine are also utilized to heat the lubricating oil of the main engine. When desired, an external load is applied to the crank shaft of the auxiliary engine to increase the heat output generated by the auxiliary engine.

What is needed is an auxiliary power unit heating system, and more particularly, an auxiliary power unit heating system comprising a means for selectively isolating a cabin heating unit in the auxiliary power unit heating system from a main engine coolant system while also providing heating capability for the main engine. The present invention meets this need.

SUMMARY OF THE INVENTION

The primary aspect of the invention is to provide an auxiliary power unit heating system, and more particularly, an auxiliary power unit heating system comprising a means for selectively isolating a cabin heating unit in the auxiliary power unit heating system from a main engine coolant system while also providing heating capability for the main engine.

Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.

The invention comprises an engine heating system for vehicles comprising an engine, a vehicle compartment heating system including fluid conduits extending from the engine to a heating unit and extending back to the engine, an auxiliary power unit on the vehicle including an auxiliary engine having a water pump driven by the auxiliary engine including fluid conduits extending from the auxiliary engine to a second heating unit located in a compartment of the vehicle and extending back to the auxiliary engine, fluid conduits extending from the engine to the second heating unit and extending back to the engine, a valve disposed in the fluid conduit between the second heating unit and the engine, the valve capable of receiving a signal, a temperature switch for detecting a coolant temperature, the temperature switch providing a signal to operate the valve, the valve allowing coolant circulation through the second heating unit to the main engine when the main engine is in operation or the coolant temperature is greater than a predetermined temperature, and the valve closed when the main engine is not in operation or the coolant temperature is below a predetermined temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.

FIG. 1 is a schematic diagram of the auxiliary power unit heating system.

FIG. 2 is a schematic diagram of the valve position versus coolant temperature.

FIG. 3 is a schematic diagram of the coolant flow when the auxiliary power unit is running and the coolant temperature is low.

FIG. 4 is a schematic diagram of the coolant flow when the auxiliary power unit is running and the cabin area is warm.

FIG. 5 is a schematic diagram of the system instrumentation.

FIG. 6 is a chart of various system and environmental temperatures.

FIG. 7 is a chart of example coolant flow rates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram of the auxiliary power unit heating system. The system comprises an auxiliary engine 100, a main engine 200, a rear heating unit 300 and a front heating unit 400.

The auxiliary engine comprises a single or multi-cylinder internal combustion or diesel engine. The auxiliary engine uses the same fuel as the main engine, for example either diesel fuel or gasoline. The auxiliary engine is cooled by a conventional water jacket coolant system. The coolant system further comprises multiple fluid conduits (pipes) within which flows a fluid such as water mixed with a suitable proportion of glycol or equivalent type anti-freeze.

The coolant system further comprises a radiator 500 to which the fluid conduits for the main engine and the auxiliary engine are connected. The radiator disposes of system waste heat when either the auxiliary engine or main engine is operating and thermostat 600 is open allowing coolant flow to the radiator.

Main engine 200 is a known form of multi-cylinder diesel or internal combustion engine comprising reciprocating pistons, cylinders and so on. Main engine 200 comprises a block which is cooled by a conventional coolant system comprising a fluid such as water mixed with a suitable proportion of glycol or equivalent type anti-freezes.

A thermostat 600 controls flow of the coolant though the radiator 500. The thermostat is known in the art and is activated based upon the temperature of the coolant circulating in the system. The thermostat opens upon reaching a predetermined temperature, for example, 180° F. The thermostat is known in the art and may either be mechanical or electrically controlled.

The coolant system comprises input fluid conduit 301 and output conduit 302 from rear heating unit 300. Rear heating unit 300 is used to provide heat to a vehicle compartment, for example, the sleeper area of a long haul truck's cabin. A normally open valve (NOV) 700 is placed in the return conduit 303 which returns the coolant to the main engine 200 after it has passed through rear heating unit 300. However, valve 700 could also be placed in output conduit 304 between the main engine 200 and rear heating unit 300 and the system function will be identical in either configuration as described herein.

Temperature switch 800 is located in conduit 301. Conduit 301 is connected to conduit 304 and conduit 309. Conduit 301 supplies coolant to the rear heating unit 300. Temperature switch 800 controls the state of valve 700, that is, it controls whether valve 700 is open or closed based upon the temperature of the coolant and the state of relay 801.

Main Engine Operating

In the mode when the main engine 200 is running, main engine water pump 201 pumps coolant to front heating unit 400 through conduit 305 and the return flow returns to the main engine 200 through conduit 306. Coolant also flows through conduit 304 toward the rear heating unit 300. Some coolant flowing toward rear heat unit 300 simultaneously flows into the auxiliary engine 100 through conduit 309. At a predetermined temperature thermostat 600 opens and a portion of the coolant flow then also flows through radiator 500. The return flow from the auxiliary engine and the radiator collects into conduit 308 and flows to conduit 307.

The coolant leaving rear heating unit 300 through conduit 307 and the auxiliary engine 100 and the radiator through conduit 308, flows through valve 700 and conduit 303 to return to the main engine 200 to repeat the cycle.

When the main engine 200 is operating, electrical relay 801 is normally open thereby preventing electrical power from reaching temperature switch 800, and consequently valve 700 in the case when temperature switch 800 is closed. However, even in the case when temperature switch 800 is closed because the coolant temperature is above its predetermined temperature set point, for example 180° F., in the case when the main engine 200 is operating and the relay 801 is open no power will flow to the valve 700, thereby assuring that normally open valve 700 remains open.

In the operating mode where only the main engine is operating, the advantage of having some coolant flow through the auxiliary engine is that the auxiliary engine will stay warmed even though it is not operating. This assures an easy start when the auxiliary power unit is required to provide to operate and heat.

Water pump 101 and water pump 201 are each “flow-through” pumps, known in the art. This means each does not significantly restrict fluid flow though the pump when the pump is not rotating, for example, when either the auxiliary engine or the main engine is not operating but fluid is still flowing through the system.

Auxiliary Engine Operating/Main Engine Shut Down

When the main engine is shut down, for example, when the vehicle is parked, and the auxiliary power unit is started, relay 801 closes (main engine off) thereby providing electrical power to temperature switch 800. Power to temperature switch 800 does not necessarily mean that valve 700 is energized. Temperature switch 800 operation, and thereby valve 700 operation in part, is dependent upon coolant temperature.

If the vehicle has not been operating for a period of time and the coolant is cold, for example, below the temperature switch lower temperature threshold ˜150° F., temperature switch 800 will be closed as demonstrated in the switch logic in FIG. 2. FIG. 2 is a schematic diagram of the valve position versus coolant temperature.

In this situation auxiliary engine 100 is started and the coolant begins circulating. Until the temperature switch upper limit (˜180° F.) has been exceeded by circulation of the steadily warming coolant, the closed temperature switch 800 provides power to the normally open valve 700, causing valve 700 to be closed and thereby stopping return coolant flow through conduit 303 to main engine 200. This isolates the auxiliary engine 100 and rear heating unit 300 from the rest of the coolant system, thereby speeding heating of the relatively smaller volume of the auxiliary engine portion of the cooling system. This configuration is shown in FIG. 3. FIG. 3 is a schematic diagram of the coolant flow when the auxiliary engine is running and the coolant temperature is low.

With valve 700 closed coolant circulates from the auxiliary engine 100 to rear heating unit 300 and back to the auxiliary engine 100. A portion of the coolant may also circulate through radiator 500 depending upon the temperature set point for thermostat 600. Since the amount of coolant circulating in this configuration is less than the total system volume, the coolant will heat up relatively quickly to provide heat to the cabin. On the other hand, if the entire volume of the coolant in the system had to be heated as in a prior art system, the temperature of the coolant will rise very slowly because of the limited heat production of the auxiliary engine. Consequently, it would take a relatively longer time to heat the cabin and sleeper area.

Once the temperature of the coolant rises above the upper temperature threshold (˜180° F.) temperature switch 800 opens thereby denergizing valve 700 which causes valve 700 to open since it is a normally open valve (NOV), i.e., energizing valve 700 closes valve 700.

With valve 700 open the auxiliary engine 100 pumps coolant through conduit 309 and conduit 301 to rear heating unit 300 and to the main engine through conduit 304. The coolant flow from rear heating unit combines with flow from conduit 303 returning from the main engine 200. The combined flow returns to the auxiliary engine through conduit 307. This is shown in FIG. 4. FIG. 4 is a schematic diagram of the coolant flow when the auxiliary power unit is running and the cabin area is warm.

The coolant returning from the main engine 200 mixes with the return coolant from rear heating unit 300 which then flows back into the auxiliary engine water pump 101. Since valve 700 is open and hot coolant from the rear heating unit 300 and cold coolant from the main engine 200 is mixing, the temperature of the coolant flowing through the auxiliary engine will decrease over time to a level were temperature switch 800 will close, thereby closing valve 700. This will again isolate a small volume of coolant which circulates between the auxiliary engine 100 and the rear heating unit 300. This will in turn quickly heat the coolant in the shortened loop until it is heated to the temperature where the valve 700 opens as described in this specification.

The cycle of closing and opening valve 700 will then continue based on the temperature of the coolant sensed by the temperature switch 800. This control strategy enables the heat produced by the auxiliary engine to first warm cabin sleeper area and then excess heated coolant is routed to warm the main engine 200.

In this configuration no heat is wasted by having the coolant flow through radiator 500 since the opening temperature for thermostat 600 is chosen to be above the upper closing threshold for temperature switch 800 (>˜190° F.). Of course, thermostat 600 may open in the case of an unplanned system temperature excursion.

FIG. 5 is a schematic diagram of the system instrumentation. Thermocouples are used to detect cabin interior ambient temperature 1000, exterior ambient temperature 1001, front heating unit inlet coolant temperature 1002, rear heating inlet coolant temperature 1003, coolant return temperature 1004, rear heating outlet coolant temperature 1005, thermostat outlet coolant temperature 1006 and rear heating air outlet temperature 1007. The temperature signals from each of the subject thermocouples may be used to measure system performance and may also be used by a vehicle ECU to optimize system operation. OF course, the system may also comprise minimal control intervention relying solely on the electrical operation of the temperature switch 800 and valve 700 and the thermostat set point. Example readings from the noted thermocouples for an example system are depicted in FIG. 6.

FIG. 6 is a chart of various system and environmental temperatures. The cyclic nature of system is evident as well as the rapid rise in the coolant temperature in the auxiliary engine coolant loop when only the auxiliary engine in operation. After the coolant has warmed the slow rise in the main engine temperature is demonstrated. The relatively slow rise time is due to periodic coolant flow to the front heating unit 400 from the main engine 200. In FIG. 6, the curves depicted on the chart correspond to the following data noted in FIG. 5 as follows:

Front Heater In—1002

Rear Heater Out—1005

Exterior Temp—1001

Rear Register—1007

Return Temp—1004

Thermostat Open—1006

Interior Ambient—1000

Rear Heater In—1003

The information depicted in FIG. 6 is provided only as an example and is not intended to limit the operating capabilities, characteristics or configurations of the system. The relatively steady Interior Ambient 1000 temperature is readily apparent. The cyclic nature of the system is clearly illustrated as well.

FIG. 7 is a chart of example coolant flow rates. The position of valve 700 is shown in the column marked “NO Valve”. “Flow out AE” is measured in conduit 309. “Flow into Rear Heater” is measured in conduit 301. “Flow into Main Engine” is measured in conduit 303. The flow rates are in gallons per minute. The information depicted in FIG. 7 is only presented as a non-limiting example since the coolant flow rates will vary depending upon the particular water pump curve, the dimensions of the various conduits, and any other components that may be installed in any particular the system.

Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein. 

1. An engine heating system for vehicles comprising: an engine; a vehicle compartment heating system including fluid conduits extending from the engine to a heating unit and extending back to the engine; an auxiliary power unit on the vehicle including an auxiliary engine having a water pump driven by the auxiliary engine including fluid conduits extending from the auxiliary engine to a second heating unit located in a compartment of the vehicle and extending back to the auxiliary engine; fluid conduits extending from the engine to the second heating unit and extending back to the engine; a valve disposed in the fluid conduit between the second heating unit and the engine, the valve capable of receiving a signal; a temperature switch for detecting a coolant temperature, the temperature switch in electrical communication with the valve and the temperature switch energizing the valve upon detection of a predetermined coolant temperature; the valve allowing coolant circulation through the second heating unit to the main engine when the main engine is in operation or when the coolant temperature is greater than a predetermined temperature; and the valve closed when the main engine is not in operation or when the coolant temperature is below a predetermined temperature.
 2. The engine heating system as in claim 1, wherein the temperature switch is inoperable when the engine is in operation and the temperature switch is operable when the engine is not in operation.
 3. The engine heating system as in claim 1 further comprising: a relay for energizing the temperature switch; and the relay is open during operation of the main engine.
 4. The engine heating system as in claim 1, wherein the valve is normally open. 